The present invention is related to lighter than air (LTA) vehicles and an external system for pressurization of the LTA vehicles. More specifically, the present invention relates to LTA's having at lease one lifting gas cell and at least one air cell, and the means for filling the air cell.
One of the major problems with non-rigid lighter-than-air vehicles is keeping the bag from bursting as the ambient pressure decreases with altitude or from collapsing when descending from altitude. One method of preventing such events is to incorporate envelopes or ballonets in the vehicle, which are inflatable gas bags within the Helium bag. The vehicle is designed to fly with partially inflated ballonets that can be inflated with air, causing the Helium volume to contract or, deflated, causing the Helium volume to expand. Thus, at altitude, the ballonets may be almost collapsed, providing the necessary “room” for the Helium to expand as ambient air pressure has decreased. As the vehicle descends into denser atmosphere, the ballonets are inflated to insure that the Helium gas bag does not collapse or even locally sag. Additionally, ballonets can play a roll in altitude control. An example of ballonets installed on a lighter-than-air vehicle can be found in U.S. Pat. No. 5,143,322 to E. W. Mason.
Prior art methods of pressurizing and filling the ballonets typically involved the use of ram air scoops. Examples of this type system can be found in U.S. Pat. No. 1,475,210 to R. H. Upson and U.S. Pat. No. 2,331,404 to H. R. Liebert.
In U.S. Pat. No. 1,580,004 to A. Bradford and U.S. Pat. No. 1,797,502 to C. S. Hall separate pumps are used for pressurizing the ballonets. Additionally, the Hall design provide heaters to heat the pressurized air. Since the ballonet is located in the middle of the main Helium filled gas bag, heating of the Helium could also be accomplished. The problem with these designs is that the ballonets are located centrally and fill valves and lines are, necessarily, co-located. Thus they are difficult to reach for maintenance and repair or removal. Additionally, the need for such fill valves and lines add weight.
U.S. Pat. No. 5,333,817 to J. B. Kalisz, et. al. teaches a ballonet system for a lighter-than-air-vehicle that includes the ballonet system includes a plurality of ballonets located within the gas bag positioned along the longitudinal axis and on each side of the vertical axis of the vehicle. Each of the ballonets include a flexible sheet joined at its periphery thereof to a portion of the wall of the gas bag. A ballonet pressurization system is coupled to each ballonet for pressurizing them with air that includes the portion of the wall of the gas bag forming the ballonet having a plurality of holes there through. A manifold having an inlet port is joined to the wall covering the holes therein and is adapted to diffuse the pressurized air entering therein. Also included is at least one fan having an inlet port coupled to ambient atmosphere and an outlet port coupled to the inlet port of the manifold for providing pressurized air to the interior thereof. A check valve located in the outlet port of the fan is provided for preventing air from flowing from the interior of the manifold out the inlet port of the fan. A ballonet venting system is included for venting the interior of the ballonet to ambient atmosphere. However, it does not provide for very rapid deflation of the ballonet.
Airships, including those that attain high altitude, where high altitude is generally being considered 40,000 ft and above, utilizing conventional methods suffer from several drawbacks. For example, the ballonets are made from a flexible, impermeable material that are attached to the interior of the envelope of the airship, and are utilized to store and separate air from the helium held within the remaining portion of the envelope. As the airship ascends to altitude, the air stored in each ballonet is exhausted through a number of valve/blowers, causing the ballonets to deflate. The helium within the envelope expands while the airship ascends to the desired altitude. It will be appreciated that expansion of the helium also forces air out of the ballonets. order to maintain pressure during descent, air is forced back into each ballonet using the valve/blowers causing the ballonets to inflate. Thus, it should be clear that the material comprising the ballonets traverses, or moves from a deflated condition to an inflated condition as air is blown into the ballonets. Likewise, the material comprising the ballonets moves from an inflated to a deflated condition as air is pushed out of the ballonets.
For high altitude airships, which are structures that resemble conventional airships, but may be significantly larger, the hull or envelope of a high altitude airship may comprise a volume of several million cubic feet. Due to the large variation in pressure and temperature that occurs as the high altitude airship moves from ground to high altitude and vice versa, it is required that the helium within the high altitude airship expand to a greater degree than that required by conventional airships. Additionally, a high altitude airship requires that a larger amount of air be expelled from its envelope than that of conventional airships. As such, to ascend the high altitude airship to a high altitude, large ballonets would be required to accommodate the large quantity of lifting gas expansion that would occur within the envelope of the high altitude airship. Utilizing large ballonets, however, is impractical for high altitude airships because the added weight would act to impede the attainment of high altitudes. Furthermore, because of the increased amount of material needed for the ballonets of a high altitude airship, significant bunching and twisting of the ballonet material would result when the ballonets are deflated, thus leading to an imbalanced condition within the envelope. The balance of the high altitude airship would be further hampered as the lifting gas would be free to accumulate in any region within the hull or envelope of the airship making it difficult to maintain control of the airship. For example, if the lifting gas accumulates toward the aft portion of the airship, this would cause the airship to become nose heavy, making it difficult to fly or to ascend.
US Patent Publication No. US 2007/0075186 to Marimon et al teaches a lifting gas cell system that provides a plurality of cells to distribute the lifting gas evenly along the length of the hull of the airship, to maintain the balance, stability, and control of the airship. Marimon does not show the blowers and valves for filling and emptying the cells, but suggests that it is part of the airship envelope.
Thus, there is a need for a lifting gas cell system that can accommodate the large expansion and contraction of the lifting gas that will occur inside an airship. Additionally, there is a need for a lifting gas cell system for an airship that is lightweight.